<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <script>
          let arr = [1, 2, 3, 4]

Array.prototype.getFilter = function (fn) {
  let arr = []
  for (let i = 0; i < this.length; i++) {
    if (fn(this[i], i, this)) {
      arr.push(this[i])
    }
  }
  return arr
}

newArr = arr.getFilter((item, index, arr, arr2) => {
  // console.log(index)
  return item >= 3
})
console.log(newArr)

// Array.prototype.getMap = function(fn){
//   let arr = []
//   for(let i = 0;i<this.length;i++){
//     arr.push(fn(this[i],i,this))
//   }
//   return arr
// }
// newArr = arr.getMap((item,index,arr)=>{
//   return item+1
// })
// console.log(newArr);
  </script>
</body>
</html>